Antenna for portable terminal and portable terminal using same

ABSTRACT

A dielectric resonator antenna which emits an electric wave by having a dielectric body resonate is disclosed. A magnetic material is contained in the electric body, thereby increasing the relative permeability to more than 1 and lowering the relative permittivity. Consequently, the Q-value of the resonance can be lowered while maintaining the rate of wavelength shortening. With this technique, a broadband dielectric resonator antenna can be realized.

TECHNICAL FIELD

This invention relates to an antenna for a portable terminal and aportable terminal including such an antenna.

BACKGROUND ART

As portable terminals of this type, various devices such as portabletelephones and PDAs have been proposed and widely spread. Normally,radio devices each comprising a transmitter and a receiver are mountedin the portable terminals for performing data communications withdatabases or the like or voice communications by radio. In order toperform the radio communications, these portable terminals areessentially provided with antennas, respectively.

In this case, in order to enable reception even when the portableterminals are placed in any states, i.e. in order to ensure mobility ofthe portable terminals, the antennas of the portable terminals arenormally nondirectional antennas. Therefore, as described above, theseantennas are designed so as not to impede the advantages of the portableterminals, such as the mobility.

As the nondirectional antennas for the portable terminals, use hasconventionally been made of quarter-wave grounded antennas. Further, asdescribed in Japanese Patent (JP-B) No. 2554762 (Patent Document 1),there has been proposed an antenna having a structure of a combinationof a quarter-wave grounded antenna and a helical antenna and thuscontrived to exhibit excellent reception sensitivity both duringcommunication and while on standby. The antennas of the portableterminals are each normally used for both transmission and reception.

Further, as antennas for miniaturizing the portable terminals, there arespreading dielectric resonator antennas each using a dielectric with alarge permittivity to thereby utilize a wavelength shortening effect ofshortening the wavelength to 1/√{square root over ((εμ))}.

In order to further miniaturize such dielectric resonator antennas,there are also those antennas each miniaturized by dividing in half thedielectric at an electric field symmetrical plane in a resonant state ofa signal in the dielectric and contacting a divided surface thereof witha conductive plate or grounding it via an insulator to thereby utilizethe mirror-image effect of an electric field by the conductive plate.These dielectric resonator antennas are also all nondirectional.

Japanese Unexamined Patent Application Publication (JP-A) No. H11-308039(Patent Document 2), Japanese Unexamined Patent Application Publication(JP-A) No. 2000-209020 (Patent Document 3), and Japanese UnexaminedPatent Application Publication (JP-A) No. 2000-209019 (Patent Document4) disclose dielectric resonator antennas.

However, these Patent Documents 2, 3, and 4 each only propose thedielectric resonator antenna that can be improved in characteristics byusing a dielectric having a high relative permittivity and improving themounting and shape of the dielectric, but discuss nothing aboutimproving a material of the dielectric forming the dielectric resonatorantenna, or the like.

On the other hand, Japanese Unexamined Patent Application Publication(JP-A) No. H10-107537 (Patent Document 5) discloses a surface-mount typeantenna having a radiation electrode, a feeding electrode, and a groundelectrode formed on a substrate made of a dielectric, which radiates aradio wave by using capacitive coupling between the radiation electrodeand the feeding electrode. This publication shows the surface-mount typeantenna that can achieve desired characteristics even if there isvariation in relative permittivity and relative permeability of thesubstrate and in electrode pattern.

However, this publication refers to nothing about a dielectric resonatorantenna that emits an electromagnetic wave to the exterior by radiatinga radio wave into a resonator formed by a dielectric so that theradiated radio wave resonates in the dielectric.

Here, the power most consumed in such portable terminals is transmissionpower including consumption power of the transmitters. As describedbefore, the antennas of the portable terminals have the nondirectivityas radio wave radiation characteristics thereof for ensuring themobility of the portable terminals. When the nondirectional antenna isused in this manner, since the portable terminal radiates a radio wave,i.e. transmits the power, in all directions including the directionswhere no base station exists, this serves as a cause of shortening thebattery life in the portable terminal.

As a method for solving the foregoing problem, consideration is given toa method of transmitting the power only in a desired direction where thebase station exists. By giving the directivity to the antenna of theportable terminal in this manner, it is possible to reduce thetransmission power. By the use of the directional antenna, it ispossible to realize the battery life that cannot be achieved by thetechnique using the conventional nondirectional antenna.

As the antenna that is capable of directional transmission, there is aphased array antenna, an adaptive array antenna, or the like. However,in order to use such an antenna, there arises a problem that since theantenna is designed with respect to a wavelength in the air, it cannotbe mounted to a portable terminal or the like without miniaturizing theantenna itself.

In order to miniaturize the antenna itself, there is the method of usingthe dielectric resonator antenna as shown in the foregoing PatentDocuments 2 to 4. For the miniaturization of the antenna, it isnecessary to use a dielectric having a higher permittivity. There hasarisen a problem that the change in impedance at a resonant frequencyincreases (the Q of the resonance increases) to narrow the band of theantenna.

Further, there has arisen a problem that when placing an antenna on aconductive plate and miniaturizing the antenna, since there is a highpermittivity layer, forming a resonator, between an electrode and theconductive plate, the parasitic capacitance increases to narrow the bandof the antenna.

When the band of the antenna is narrowed as described above, it ispossible to broaden the band by performing matching by a matchingcircuit that serves to supply the power to the antenna. However, therehas arisen a problem that since the band of the antenna itself isnarrow, the power loss in the matching circuit increases to reduce thebattery life of the portable terminal. That is, with respect to theconventional dielectric resonator antenna, the band of the antennaitself is narrow and, as a result thereof, there is a drawback that theloss in the matching circuit is large.

Further, since there is difficulty in realizing the efficient miniatureantenna as described above, it is hard to adopt the structure of thearray antenna or the like and, therefore, there is a problem that it isdifficult to control the directivity of the portable terminal to therebyreduce the transmission power.

DISCLOSURE OF THE INVENTION

In view of the foregoing problems, it is an object of this invention toprovide a miniaturizable antenna for a portable terminal at a low cost.

It is another object of this invention to provide a portable terminalthat can reduce the transmission power to improve the battery life.

A specific object of this invention is to provide a dielectric resonatorantenna that can be used as an antenna for a portable terminal, which iscapable of lowering the consumption power by reducing a loss in amatching circuit.

It is another object of this invention to provide a dielectric resonatorantenna that can prevent a reduction in efficiency when it is mounted toa portable terminal.

It is still another object of this invention to provide a dielectricresonator antenna that can realize low consumption power by givingdirectivity thereto.

It is another object of this invention to provide a method of designinga dielectric resonator antenna having a broad band.

According to this invention, there is provided an antenna being capableof reducing a loss in a matching circuit by broadening a band thereof.For this end, a resonator antenna of this invention has an electrodeoutside or inside an insulator material and emits a radio wave to theexterior by resonating a signal supplied into the insulator materialfrom the electrode, and is characterized in that a relative permeabilityμra of the insulator material is μra>1. Herein, the relativepermeability being μra>1 represents that the relative permeability μrais greater than 1 when a fraction below decimal point is rounded off.

On the other hand, when a first mode on the low frequency side and asecond mode on the high frequency side at resonance peaks are observedas resonant modes of the antenna, the second mode becomes strong whenμra is large, while, the first mode becomes strong when εra is large.Therefore, it is preferable that μra and εra be approximately equal toeach other and it is more preferable that values of μra and εra beadjusted so that the band can be broadened by superimposing therespective modes.

μra and εra being approximately equal to each other in this inventionrepresents that, as shown in FIG. 9, half frequencies of the resonancepeaks of the first mode on the low frequency side and the second mode onthe high frequency side are partly shared in frequency vs. antenna inputimpedance characteristics.

Further, the resonator antenna of this invention is characterized bybeing mounted on a conductive plate, operating as a reflecting plate, ina manner to contact therewith or via an insulator having a relativepermittivity εra>1.

Further, the antenna with the reflecting plate of this invention ischaracterized in that, given that a relative permeability is μrr and arelative permittivity is εrr, a magneto-dielectric layer with μrr≧εrr isprovided on a surface, opposite to an antenna mounting surface, of thereflecting plate.

A portable terminal of this invention is characterized by comprising theforegoing antenna and, particularly, it is preferable that a pluralityof the foregoing antennas be mounted.

Hereinbelow, the operation of this invention will be described.

According to the resonator antenna of this invention, since the relativepermeability μra of the dielectric (insulator) forming an antennaelement is μra>1, it is possible to increase a wavelength shorteningcoefficient √{square root over ((εra·μra))} (note: since in-resonatorwavelength λr=3×10⁸ [m/s]/f [Hz]/√{square root over ((εr·μr))} and spacewavelength λ0=3×10⁸ [m/s]/f [Hz], when the respective wavelengths aresubstituted for wavelength shortening coefficient=λ0/λr, the wavelengthshortening coefficient can be derived as the square root of the productof the relative permeability and the relative permittivity) of anelectromagnetic wave in the resonator and, as compared with the casewhere use is made of a general dielectric having μra=1, the relativepermittivity can be reduced. This makes it possible to reduce theimpedance change at the time of resonance and thus realize broadening ofthe band of the antenna.

Although the ranges of the relative permittivity and the relativepermeability are properly selected depending on communicationfrequencies, communication band, allowable component volumes, and so on,since the antenna gain is reduced when a short side of the antennaelement becomes too small, they are preferably 200 or less and morepreferably 100 or less, respectively. Further, as the wavelengthshortening coefficient, referring to FIG. 10, since the frequency rangeof the portable terminal is 800 MHz to 5.2 GHz, it is 200 or less whenthe short side of the resonator is 1 mm, 100 or less when 2 mm, andabout 50 to 3 when the short side of the resonator is set to about 5 mmor more for preventing the reduction in gain.

Further, according to the resonator antenna of this invention, thedielectric forming the antenna is mounted on a conductive plate in amanner to directly contact therewith or via an insulator with εrd>1.

In this case, the mirror-image effect of an electric field can beutilized at the electric field symmetrical plane to thereby enableminiaturization of the antenna and, further, since the permittivity ofthe antenna itself can be reduced by the effect of the permeability, theimpedance change at the time of resonance can be reduced to therebyenable broadening of the band.

Moreover, according to the antenna of this invention, themagneto-dielectric layer having a relationship of μrr>εrr where εrrrepresents the relative permeability and εrr the relative permittivity,is provided on the surface, opposite to the antenna mounting surface, ofthe reflecting plate. Therefore, the mirror-image effect is producedwith respect to a magnetic field, thereby enabling an improvement inreflection characteristics and thus in antenna gain. Therefore, theradio wave can reach a base station with small power so that the batterylife of the portable terminal can be improved.

When the antenna of this invention is employed in the portable terminal,since the antenna element itself is broadband, it is possible to reducethe loss in the matching circuit and therefore improve the battery lifeof the portable terminal.

Further, when a plurality of antennas of this invention are employed inthe portable terminal, since each antenna is highly efficient whilebeing small in size, an array antenna can be efficiently formed so thatthe direction of the radio wave transmitted from the portable terminalcan be controlled. Therefore, it is possible to suppress radiation ofthe radio wave in a direction opposite to the base station to therebyachieve the effective utilization of the power so that the battery lifeof the portable terminal can be improved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram showing a magneto-dielectric resonatorantenna according to an embodiment 1 of this invention.

FIG. 2 is a characteristic diagram showing the input impedance of themagneto-dielectric resonator antenna with respect to signal frequency inthe embodiment 1 of this invention.

FIG. 3 is a characteristic diagram showing the input impedance of amagneto-dielectric resonator antenna with respect to signal frequency inthe case where use is made of a magneto-dielectric having differentcomposition components, in the embodiment 1 of this invention.

FIG. 4 is a schematic diagram showing a resonator antenna using amagneto-dielectric according to an embodiment 2 of this invention.

FIG. 5 is a characteristic diagram showing changes in real part of theinput impedance with respect to normalized frequency normalized by aresonant frequency in the embodiment 2 of this invention.

FIG. 6 is a schematic diagram showing a resonator antenna using amagneto-dielectric according to an embodiment 3 of this invention.

FIG. 7 is a schematic diagram showing a portable terminal in anembodiment 4 of this invention.

FIG. 8 is a characteristic diagram showing a radio wave radiationpattern of the portable terminal in the embodiment 4 of this invention.

FIG. 9 is a characteristic diagram showing frequency vs. antenna inputimpedance characteristics in an antenna of this invention.

FIG. 10 is a diagram showing a relationship between frequency (MHz) andwavelength shortening coefficient, wherein there are shown wavelengthshortening coefficients when the length of a short side of a resonatorforming an antenna of this invention is changed.

BEST MODE FOR CARRYING OUT THE INVENTION Embodiment 1

A resonator antenna according to an embodiment 1 of this invention willbe described with reference to FIG. 1. FIG. 1 is a schematic diagramshowing the resonator antenna according to the embodiment 1, whereinthere are included a dielectric (insulator) 20 forming a resonator and afeeding electrode 22 for feeding the power to the resonator.

When manufacturing the illustrated magneto-dielectric 20, cobalt powderwith a diameter of 50 nm and BST (barium strontium titanate) powder witha diameter of 0.5 μm were prepared and both powders were dispersed intoan epoxy resin. In this case, 50 vol % cobalt and 10 vol % BST powderwere dispersed with respect to the epoxy resin, then subjected toburning at 200° C. for one hour, and formed into a shape with a width of14 mm, a length of 15 mm, and a thickness of 5.9 mm, thereby obtainingthe illustrated dielectric 20. As a result of measuring the permittivityand permeability of this dielectric material by the cavity resonatormethod, εra=11 and μra=9 so that a wavelength shortening coefficient ofabout 10 was obtained.

Then, by the use of silver paste, the feeding electrode 22 having awidth of 0.5 mm was formed on a long-side surface of a rectangularparallelepiped by the photolithography method, thereby forming themagneto-dielectric antenna shown in FIG. 1.

FIG. 2 shows frequency characteristics of the impedance when a signal issupplied to the feeding electrode 22 by the use of a network analyzer.In FIG. 2, the real part of the input impedance is plotted againstfrequency and, for comparison, the impedance of an antenna of the samesize made of BST (εra=100, μra=1) is shown.

By the inclusion of the magnetic material, a resonant mode on the lowfrequency side and a resonant mode on the high frequency side wereexcited at substantially the same frequencies so that the band of theantenna was able to be broadened.

In order to understand the effect of this invention in more detail,cobalt powder and BST powder were dispersed into an epoxy resin in theratio of 30 vol % and 20 vol %, respectively, thereby obtaining amagneto-dielectric 20 having εra=20 and μra=5. Like in the case of theforegoing dielectric 20, a feeding electrode with a width of 0.5 mm wasformed on this magneto-dielectric 20 by the use of silver paste, therebyobtaining a resonator antenna.

FIG. 3 shows characteristics of the real part of the input impedance ofthis resonator antenna with respect to frequency. It is understood thata resonant mode on the low frequency side and a resonant mode on thehigh frequency side exist in a separated state in terms of frequency.That is, it is understood that the resonant frequency can be controlledby controlling μra.

According to the resonator antenna of this invention using themagneto-dielectric, the resonator is made of the magneto-dielectricformed by mixing together the dielectric and the magnetic material,wherein the resonant frequency can be controlled by controlling εra andμra and, further, the resonant modes can be superimposed by setting εraand μra to be substantially equal to each other, thereby enabling theband of the antenna to be broadened.

Further, according to the resonator antenna of this invention, byintroducing the magnetic material into the dielectric, the permittivitycan be reduced and thus the Q value of the resonance can be loweredwhile maintaining the wavelength shortening coefficient given by√{square root over ((εra·μra))}, thereby enabling the band to bebroadened.

Further, when the resonator antenna of this invention is mounted to aportable terminal, since the band of the antenna itself can bebroadened, a loss in a matching circuit can be reduced so that it ispossible to improve the battery life.

Embodiment 2

Referring to FIG. 4, description will be given of a resonator antennausing a magneto-dielectric in an embodiment 2 of this invention.

The resonator antenna according to the embodiment 2 shown in FIG. 4comprises a resonator formed by a magneto-dielectric 20, which resonatesa signal and emits it as a radio wave into the space, a feedingelectrode 22 for feeding a signal to the resonator, a printed wiringboard 24 for mounting thereon a body of the resonator, and a metal plate26 which is located on a surface of the printed wiring board 24 on itsside opposite to the antenna and terminates an electric field from theantenna so as to make a mirror image of the electric field. In thisembodiment, a copper plate is used as the metal plate 26.

According to the same method as that in the embodiment 1, there wasformed the resonator of the magneto-dielectric 20 having a width of 14mm, a length of 15 mm, a thickness of 5.9 mm, εra=11, and μra=9 and thenthe feeding electrode 22 with a width of 0.5 mm was formed by the use ofsilver paste. This antenna element was mounted at the center of theprinted wiring board 24 having a width of 5 cm, a length of 5.3 cm, anda thickness of 0.1 mm and formed with a silver foil film having athickness of 30 μm on the surface thereof opposite to its surface wherethe antenna was to be mounted.

FIG. 5 shows changes in input impedance, with respect to frequency, ofthe antenna mounted on the board having the metal reflecting plate 26formed as described above. FIG. 5 shows changes in real part of theinput impedance with respect to normalized frequency that was normalizedby a resonant frequency, wherein there are shown, for comparison,relevant changes with respect to the resonator antenna (εra=100, μra=1)made of BST as described in relation to the embodiment 1, which ismounted on the same board.

As also clear from FIG. 5, it is understood that when the antenna ofthis embodiment is used, εra can be reduced by the use of themagneto-dielectric and thus the Q value of the resonance can be lowered,thereby enabling the antenna band to be broadened.

According to the resonator antenna mounted on the board having the metalreflecting plate 26 in this embodiment, since the Q value of theresonance can be reduced even when mounted on the reflecting plate, theband can be broadened and, therefore, when it is mounted to a portableterminal, a loss in a matching circuit serving to broaden the band canbe reduced so that it is possible to improve the battery life of theportable terminal.

Embodiment 3

Referring to FIG. 6, description will be given of a resonator antennausing a magneto-dielectric in an embodiment 3 of this invention. Theresonator antenna according to the embodiment 3 shown in FIG. 6comprises a resonator formed by a magneto-dielectric 20, which resonatesa signal and emits it as a radio wave into the space, a feedingelectrode 22 for feeding a signal to the resonator, a printed wiringboard 24 for mounting thereon a body of the resonator, and a magneticlayer 28 which is located at a surface of the printed wiring board 24 onits side opposite to the antenna and formed at the surface thereofopposite to its surface where the antenna is mounted.

Like in the embodiment 2, the resonator was formed by themagneto-dielectric 20 having a width of 14 mm, a length of 15 mm, athickness of 5.9 mm, εra=11, and μra=9. The magneto-dielectric 20 wasmounted, as an antenna element, on the printed wiring board 24 having awidth of 5 cm, a length of 5.3 cm, and a thickness of 0.1 mm. In thiscase, a copper foil film having a thickness of 30 μm had been formed onthe surface, opposite to the antenna mounting surface, of the printedwiring board 24. By mounting the magneto-dielectric 20 at the center ofthe printed wiring board 24, the resonator antenna with the reflectingplate was formed. Further, on the surface, opposite to the antennamounting surface, of the illustrated resonator antenna, the magneticplate 28 having a relative permittivity of 4 and a relative permeabilityof 10 was formed to a thickness of 5 mm. In this case, the magneticplate 28 was formed by dispersing cobalt powder with a diameter of 50 nminto an epoxy resin in the ratio of 50 vol % by the use of the solutioncast method and then drying them at 200° C. for 30 minutes.

As a result of forming a thin film with a thickness of 5 mm under thesame conditions as the forming conditions of the foregoing magneticplate 28 and measuring its relative permittivity and permeability by theuse of an impedance material analyzer, the subject magnetic plate 28 hada relative permittivity of 4 and a relative permeability of 10.

An evaluation was made of changes in input impedance of the thus formedantenna when mounted to a portable terminal. The antenna in the portableterminal was evaluated as changes in impedance depending on the presenceof an influence of a human head. The evaluation results are shown inTable 1. TABLE 1 Human Head present (Interval to Antenna Antenna alone10 mm) Magneto-dielectric Resonator  157.8-105.9i 150.1-112.2i Antenna(with Magnetic Plate) (Embodiment 3) Monopole Antenna 109.1-39.5i180.5-14.8i  Magneto-dielectric Resonator 108.7-68.6i  98.6-107.6iAntenna (with Magnetic Plate) (Embodiment 2)

Table 1 shows changes in impedance depending on the presence of thehuman head when the foregoing antenna was mounted to the portableterminal and, for comparison, also shows changes in impedance of amonopole antenna hitherto used in a portable terminal and of theresonator antenna with the reflecting plate shown in the embodiment 2.The measurement frequency was set to 2 GHz. It is understood that theimpedance is reluctant to change even with the presence of the humanhead when the magnetic plate 28 is provided on the back side of themetal reflecting plate 26.

In the resonator antenna according to the embodiment 3, the inputimpedance is reluctant to be affected by the human head. Consequently,it was possible to reduce reflection of an input signal at the feedingelectrode 22 caused by mismatching with a matching circuit and, as aresult, it was possible to reduce a loss in the matching circuit.

Embodiment 4

Referring to FIG. 7, description will be given of a portable terminal inan embodiment 4 of this invention. A portable terminal antenna accordingto the embodiment 4 shown in FIG. 7 is used as a signal transmissionantenna of the portable terminal and, in this example, two antennas eachwith a reflecting plate, shown in the embodiment 2, are mounted. Arectangular board mounted thereon with the antenna comprises a printedwiring board 24 having a width of 5 cm and a length of 10 cm and a metalplate 26 provided on a surface of the printed wiring board 24 on itsside opposite to an antenna mounting surface thereof. The two antennaelements each formed by a dielectric 20 and a feeding electrode 22 aredisposed along a center line located at a distance of 25 cm from bothshort sides and at an interval of 5 cm from each other in a long-sidedirection.

FIG. 8 shows a radiation pattern when in-phase signals are supplied tothe foregoing two antenna elements to cause them to perform the phasedarray operation. As shown in FIG. 8, the antenna of the embodiment 4 hasdirectivity and, as compared with the case of the single antenna, it canimprove the gain and control a radio wave radiation direction toward abase station direction. Therefore, the antenna shown in FIG. 7 does nottransmit useless power into the space. As a result, it was possible toreduce the consumption power in the portable terminal to thereby improvethe battery life.

The battery life improving effect in this embodiment is shown in Table2. TABLE 2 Battery Life Portable Terminal in Embodiment 4(Magneto-dielectric 662 min. Resonator Antenna with Magnetic Layer)Conventional Portable Terminal Monopole Antenna 144 min.

As also clear from Table 2, it is understood that the portable terminalaccording to the embodiment 4 of this invention is largely improved inbattery life as compared with the conventional portable terminal. Thisshows that, by using the resonator antenna employing themagneto-dielectric like in this invention, the miniature broadbandantenna with high efficiency was able to be formed because the Q valueof the resonance did not increase even using the reflecting plate.

In the foregoing embodiments, the description has been given of only theexample where cobalt is used as the magnetic material forming themagneto-dielectric 20. However, the magnetic material to be contained inthe dielectric material may be a simple substance of cobalt, manganese,or iron, or an alloy or compound magnetic material containing at leastone of cobalt, manganese, and iron. For example, there are cited analloy of cobalt and iron, an alloy of a rare earth element and iron,ferrite, and so on. Further, these magnetic materials may be compoundedor mixed together so as to be used. In the embodiments, the descriptionhas been given of the example where the dielectric material is obtainedby dispersing the BST powder into the epoxy resin. However, as thedielectric material, a dielectric material having a desired permittivitycan be properly selected and used, which may be mixed with the magneticmaterial. As the dielectric material, use may be made of, alone or in amixed manner, organic materials (resin materials) such as, for example,liquid crystal resin, epoxy resin, olefin-based resin, fluororesin, BT(bismaleimide triazine) resin, and polyimide resin, or use may be madeof, alone or in a compounded or mixed manner, inorganic materials suchas silica (SiO₂, SiO), silicon nitride (SiN, Si₃N₄), zirconia (ZrO,ZrO₂), hafnia (HfO, HfO₂), titania (TiO, TiO₂), aluminum nitride (AlN),SrBi₂Ta₂O₉, SrBi₂(Ta_(1-x),Nb_(x))₂O₉, and Sr₂(Ta_(1-x),Nb_(x))₂O₇. Asthe inorganic dielectric material, use may also be made of, alone or ina compounded or mixed manner, high permittivity materials such as PZT(lead zirconate titanate), alumina (Al₂O₃), BiTiO₃, SrTiO₃, PbZrO₃,PbTiO₃, and CaTiO₃. The inorganic dielectric materials of the foregoingtwo examples may be used in a mixed manner, or the inorganic dielectricmaterials alone or in a compounded or mixed manner and the organicdielectric materials alone or in a mixed manner may be used in a mixedmanner. The magnetic material is mixed into, preferably the fine powderof the magnetic material is dispersed into, the dielectric material tothereby obtain the magneto-dielectric. In this case, the relativepermeability of the magneto-dielectric preferably exceeds 1 and is about50 (preferably 15).

According to the resonator antenna of this invention, since the relativepermeability μra of the insulator forming the antenna element is μra>1,it is possible to increase the wavelength shortening coefficient1/√{square root over ((εra·μra))} of the electromagnetic wave in theresonator and, as compared with the case where use is made of thegeneral dielectric having μra=1, the relative permittivity can bereduced. This makes it possible to reduce the impedance change at thetime of resonance and thus realize broadening of the band of theantenna.

Further, according to the resonator antenna of this invention, since theantenna contacts with the conductive plate or is grounded via theinsulator having εrd>1, the mirror-image effect of the electric fieldcan be utilized at the electric field symmetrical plane to therebyenable miniaturization of the antenna and, further, since thepermittivity of the antenna itself can be reduced by the effect of thepermeability, the impedance change at the time of resonance can bereduced to thereby enable broadening of the band.

Moreover, according to the antenna of this invention, themagneto-dielectric layer having μrr≧εrr where μrr represents therelative permeability and εrr the relative permittivity, is provided onthe surface, opposite to the antenna mounting surface, of the reflectingplate so that the mirror-image effect is produced with respect to themagnetic field, thereby enabling the improvement in reflectioncharacteristics and thus in antenna gain. Therefore, the radio wave canreach the base station with small power so that the battery life of theportable terminal can be improved.

When the antenna of this invention is employed in the portable terminal,since the antenna element itself is broadband, it is possible to reducethe loss in the matching circuit and therefore improve the battery lifeof the portable terminal.

Further, when a plurality of antennas of this invention are employed inthe portable terminal, since each antenna is highly efficient whilebeing small in size, the array antenna can be efficiently formed so thatthe direction of the radio wave transmitted from the portable terminalcan be controlled. Therefore, it is possible to suppress radiation ofthe radio wave in a direction opposite to the base station to therebyachieve the effective utilization of the power so that the battery lifeof the portable terminal can be improved.

1. A dielectric resonator antenna comprising a dielectric made of aninsulator material and an electrode provided outside or inside saiddielectric, said dielectric resonator antenna being adapted to emit aradio wave to the exterior by resonating a signal supplied into saiddielectric from said electrode, said dielectric having a relativepermeability (μra) of μra>1.
 2. The dielectric resonator antennaaccording to claim 1, wherein said dielectric is mounted on a conductiveplate, provided as a reflecting plate, directly or via an insulatorhaving a relative permittivity εrd>1.
 3. The dielectric resonatorantenna according to claim 2, wherein, given that a relativepermeability is εrr and a relative permittivity is εrr, amagneto-dielectric layer having a relationship of εrr≧εrr is provided ona surface, opposite to a dielectric mounting surface, of said reflectingplate.
 4. The dielectric resonator antenna according to claim 1, whereinsaid dielectric contains a magnetic material and a dielectric material.5. A dielectric resonator antenna comprising a resonator formed by theuse of a dielectric having a relative permittivity and a relativepermeability that realize frequency vs. antenna input impedancecharacteristics so as to partly share half frequencies of resonancepeaks of a first mode on a low frequency side and a second mode on ahigh frequency side.
 6. The dielectric resonator antenna according toclaim 4, wherein a wavelength shortening coefficient is 200 or less. 7.The dielectric resonator antenna according to claim 4, wherein awavelength shortening coefficient is 100 or less.
 8. The dielectricresonator antenna according to claim 4, wherein a wavelength shorteningcoefficient is 50 to
 3. 9. The dielectric resonator antenna according toclaim 4, wherein said magnetic material contains at least one of asimple substance of cobalt, manganese, or iron, and an alloy and acompound magnetic material each containing at least one of cobalt,manganese, and iron.
 10. The dielectric resonator antenna according toclaim 4, wherein said dielectric material contains one or both of aresin material containing at least one of liquid crystal resin, epoxyresin, olefin-based resin, fluororesin, BT (bismaleimide triazine)resin, and polyimide resin and an inorganic dielectric materialcontaining at least one of silica (SiO₂, SiO), silicon nitride (SiN,Si₃N₄), zirconia (ZrO, ZrO₂), hafnia (HfO, HfO₂), titania (TiO, TiO₂),aluminum nitride (AlN), SrBi₂Ta₂O₉, SrBi₂(Ta_(1-x),Nb_(x))₂O₉,Sr₂(Ta_(1-x),Nb_(x))₂O₇, BST (barium strontium titanate), PZT (leadzirconate titanate), alumina (Al₂O₃), BiTiO₃, SrTiO₃, PbZrO₃, PbTiO₃,and CaTiO₃.
 11. The dielectric resonator antenna according to claim 10,wherein fine powder of said magnetic material is dispersed into saidresin material.
 12. The dielectric resonator antenna according to claim11, wherein said inorganic dielectric material is further dispersed intosaid resin material.
 13. The portable terminal including the dielectricresonator antenna according to claim
 1. 14. The portable terminalincluding a plurality of dielectric resonator antennas each according toclaim 1 and being capable of adjusting a radio wave radiation direction.15. A method of manufacturing a dielectric resonator antenna that emitsa radio wave by radiating a radio wave to a resonator formed by adielectric and resonating said radiated radio wave in said dielectric,said method comprising: adjusting a relative permittivity on conditionthat a relative permeability exceeds 1, to thereby obtain amagneto-dielectric material that can achieve a predetermined wavelengthshortening coefficient; and forming said dielectric by the use of saidmagneto-dielectric material.
 16. The method according to claim 15,wherein said magneto-dielectric material is produced by mixing togethera magnetic material and a dielectric material.
 17. The method accordingto claim 16, wherein said magnetic material contains at least one of asimple substance of cobalt, manganese, or iron, and an alloy and acompound magnetic material each containing at least one of cobalt,manganese, and iron.
 18. The method according to claim 16, wherein saiddielectric material contains one or both of a resin material containingat least one of liquid crystal resin, epoxy resin, olefin-based resin,fluororesin, BT (bismaleimide triazine) resin, and polyimide resin andan inorganic dielectric material containing at least one of silica(SiO₂, SiO), silicon nitride (SiN, Si₃N₄), zirconia (ZrO, ZrO₂), hafnia(HfO, HfO₂), titania (TiO, TiO₂), aluminum nitride (AlN), SrBi₂Ta₂O₉,SrBi₂(Ta_(1-x),Nb_(x))₂O₉, Sr₂(Ta_(1-x),Nb_(x))₂O₇, BST (bariumstrontium titanate), PZT (lead zirconate titanate), alumina (Al₂O₃),BiTiO₃, SrTiO₃, PbZrO₃, PbTiO₃, and CaTiO₃.
 19. The method according toclaim 18, further comprising dispersing fine powder of said magneticmaterial into said resin material.
 20. The method according to claim 19,further comprising dispersing said inorganic dielectric material intosaid resin material.